A turbine engine such as a turboprop or an unducted turbofan known as a UDF for “unducted fan” comprises one or more propellers, a propeller consisting in a disk with airfoils mounted on a hub that can rotate about a shaft. A set of two propellers forms a corotating or contrarotating propfan depending on whether the two propellers rotate in the same direction or in opposite directions. One of the main sources of excitation of the airfoils originates from the wakes and the pressure fluctuations generated by the obstacles adjacent to the propeller.
The coupling structure, most frequently in the form of a mast, by which the engine is attached, upstream or downstream of the propeller depending on the architecture, to the aircraft, forms the main obstacle generating turbulence in the flow. The movement of the airfoils of the propeller in this turbulence creates a synchronous harmonic excitation of the speed of rotation of the propeller concerned and generates an instationary pressure field on the surface of the airfoils.
In the field of aviation turbine engines, the vanes or airfoils are particularly sensitive parts because they must satisfy, in terms of design, imperatives of aerodynamic and aeroacoustic performance and of mechanical strength in rotation, temperature and aerodynamic load. All these aspects mean that these structures are fairly highly loaded statically and that, because of the imperatives of service life, the vibrational amplitudes that they sustain must remain low. Moreover, the aeroelastic coupling, that is to say the coupling between the dynamics of the propellers and the fluid flow, is a condition of the vibrational stability of the structure.
Within the context of the design of a turbine engine, and because of the multidisciplinarity of those involved, the design process is iterative. The vibrational design is carried out in order to prevent the presence of critical resonances in the operating range of the machine. The assembly is validated at the end of the design cycle by an engine test in which the vibrational amplitudes are measured. High vibrational levels associated either with resonances or with vibrational instabilities sometimes occur. The fine-tuning of the disk concerned must then be repeated, which is particularly protracted and costly.
The object of the present invention is to control, as early as during the design or development phase of the machine, the vibrational response levels of the airfoils in a turbine-engine structure comprising at least one moveable propeller and one fixed obstacle formed by the coupling structure, traversed by air.